1. Field of the Invention
The present invention relates to aligned fine particles in which fine particles whose surfaces are coated with an organic coating film are aligned on a surface of a substrate, a method for producing the same and a device using the same. The present invention also relates to industrial applications thereof, that is, a magnetic recording medium for high density magnetic recording/reproduction in which fine magnetic particles are aligned on a substrate, a magnetoresistive device, and a semiconductor device utilizing fine particles.
2. Description of the Related Art
There have been methods for forming fine particles on a surface of a substrate for a long time. Conventional and typical techniques include a method of dipping a substrate in a fine particle solution in which fine particles are dispersed, a method of dripping fine particles on a surface of a substrate for bar coating, and a method of dripping a fine particle solution as above on a surface of a substrate and then applying it over the surface by rotation.
Furthermore, a method for forming an organic thin film on surfaces of fine particles has been under development for a few years. JP1(1989)-309902A discloses a method of coating surfaces of fine particles with an organic material comprising a chlorosilane compound or the like, and a method for forming a film made of fine particles on a surface of a substrate. In addition, it recently has been reported in a scientific magazine (Science, Mar. 17, 2000) that a monomolecular film-like film is formed on surfaces of fine particles, and they are formed on a surface of a substrate. This method has broken the limit of the crystal grain size control of a conventional thin film magnetic recording medium, and has received attention as an attempt to control magnetic domains by the size of the fine particles.
A method for forming a pattern of fine particles is disclosed in JP2(1990)-9196.
A tunnel magnetoresistive device utilizing fine particles has been proposed (Science, vol. 290, Nov. 10, 2000, page 1131).
In the field of semiconductor devices, dot memory devices employing nanoparpticles as their floating gates are expected to serve as a high-speed operable non-volatile memory (e.g., S. Tiwari et al. Applied Physics Letter, vol. 68, page 1377, 1996). In the dot memory devices, metallic or semiconductor fine particles of several nm or less are used to carry charges.
However, none of the conventional and typical techniques such as dipping a substrate in a fine particle solution in which fine particles are dispersed, dripping fine particles on a surface of a substrate for bar coating, and dripping the fine particle solution on a surface of a substrate and then applying it over the surface by rotation can control the thickness of the fine particles on the order of the fine particle size. In addition, as the fine particle size becomes smaller, the distribution of the thickness of the fine particles on the surface of a substrate becomes larger.
JP 1(1989)-309902 is valuable as a basic patent for coating the surfaces of fine particles with a monomolecular film, but fails to disclose a method for immobilizing the fine particles on the surface of a substrate, and thus presumably has problems in the practical use, the production, and the durability.
In the above-described article (Science, Mar. 17, 2000), a method for controlling the thickness of a film comprising fine particles is not established, and this article only discloses that fine particles are placed on the surface of a substrate as in the above-described patent and seems to have a problem in adhesion between the substrate and the fine particles and thus a large problem in the practical use, the production, and the durability. When producing a magnetic recording medium by such a method, it is difficult to apply fine particles in a uniform thickness on the entire area of a HDD drive (at least 1 square inch) that is in practical use at present.
In the conventional methods, only one type of fine particles is used. However, not only one type but a plurality of types of fine particles may be required to produce a functional device. There is no disclosure or conception of such a method in the prior art.
JP2(1990)-9196 is valuable as one approach for forming a pattern of fine particles, but fails to disclose coupling between fine particles and a substrate as in the above-described patent and article, so that this also seems to have problems in the practical use, the production, and the durability.
Also when forming a magnetoresistive device employing fine particles, it is important to disperse the controlled number of layers of fine particles having uniform sizes.
When applying this technique of employing fine particles to semiconductors, it is essential to form ultrafine particles having uniform particle sizes in a high density and uniformly on a tunnel insulating layer. However, the conventional techniques have not succeeded at it.